依合2A井志留系柯下段致密含油砂岩储层特征

致密砂岩油藏是塔里木盆地石油增储上产的重要资源基础之一。台盆区志留系柯下段是近几年新发现的一套海相碎屑岩含油气储盖组合,储层为典型致密砂岩。依合2A井是新钻探的一口重要的区域探井,该井在志留系柯下段获良好油气显示,通过该井系统取心、取样分析,使深入研究这套致密储层特征成为可能。通过对岩心样品进行岩石薄片、物性、铸体薄片、扫描电镜、高压压汞和黏土矿物等系统测试分析,详细研究了柯下段致密含油砂岩储层特征及其主控因素。研究表明,柯下段致密砂岩储层主要为细粒、细—中粒岩屑砂岩,岩屑含量高,成分成熟度低,结构成熟度中等；为特低—超低孔、特低—超低渗储层；孔隙类型主要为晶间孔、粒内孔等微孔隙,次为粒间孔；孔喉结构为细孔 —微孔微细喉型,根据毛细管压力曲线的特点可分为4类。造成储层致密的主要控制因素是强烈的压实作用和胶结作用以及较弱的溶解作用,使得孔隙不发育,同时黏土矿物含量较高,孔隙空间和结构进一步变差,储层渗透性进一步降低,并具较强敏感性。

Reservoir Characteristics of Tight Oil-bearing Sandstone of Lower Member in Kepingtage Formation of Silurian in Well Yihe2A

Tight sand reservoir is one of the important resources for increasing oil reserves and production in Tarim Basin. The lower member of Silurian Kepingtage Formation in the platform-basin is a newly discovered oil-and-gas reservoir-caprock assemblage of marine clastic rocks in recent years. It is a typical tight sandstone reservoir. Well Yihe2A is a new important regional prospecting well which presents a good show of oil and gas in the lower member of Silurian Kepingtage Formation. Through systematic coring and sampling analysis, it gets feasible to study the characteristics of the tight sandstone. The characteristics and main controlling factors of the tight oil-bearing sandstone reservoir are studied in details by means of rock core system testing analysis such as rock thin section, physical property, cast thin section, scanning electron microscope, conventional mercury penetration, clay mineral and etc. It shows that the tight sandstone reservoirs of lower member have high lithic content, low compositional maturity and medium structure maturity dominated to be fine grained lithic sandstone and fine-medium grained lithic sandstone. It is super low to ultra low porosity and permeability. The pore of the reservoirs is mainly of micro-pore with intercrystalline pore, intraparticle pore and etc. At the same time, the minor pore is intergranular pore. The pore-throat structure is punctate to microbore throat. The reservoir can be divided into four categories by the characteristics of the capillary pressure curve. The strong compaction, cementation and weak dissolution are the main factors resulting in the tight reservoir with low porosity and low permeability, while the high content of clay minerals makes the pore space and structure further deteriorate, and the permeability of the reservoir further reduces. And the reservoir has strong sensitivity.